This invention relates generally to image producing machines, and more particularly to a solid phase change ink pre-melter assembly and a phase change ink image producing machine or printer having same.
In general, phase change ink image producing machines or printers employ phase change inks that are in the solid phase at ambient temperature, but exist in the molten or melted liquid phase (and can be ejected as drops or jets) at the elevated operating temperature of the machine or printer. At such an elevated operating temperature, droplets or jets of the molten or liquid phase change ink are ejected from a printhead device of the printer onto a printing media. Such ejection can be directly onto a final image receiving substrate, or indirectly onto an imaging member before transfer from it to the final image receiving media. In any case, when the ink droplets contact the surface of the printing media, they quickly solidify to create an image in the form of a predetermined pattern of solidified ink drops.
An example of such a phase change ink image producing machine or printer, and the process for producing images therewith onto image receiving sheets is disclosed in U.S. Pat. No. 5,372,852 issued Dec. 13, 1994 to Titterington et al. As disclosed therein, the phase change ink printing process includes raising the temperature of a solid form of the phase change ink so as to melt it and form a molten liquid phase change ink. It also includes applying droplets of the phase change ink in a liquid form onto an imaging surface in a pattern using a device such as an ink jet printhead. The process then includes solidifying the phase change ink droplets on the imaging surface, transferring them the image receiving substrate, and fixing the phase change ink to the substrate.
Conventionally, the solid form of the phase change is a xe2x80x9cstickxe2x80x9d, xe2x80x9cblockxe2x80x9d, xe2x80x9cbarxe2x80x9d or xe2x80x9cpelletxe2x80x9d as disclosed for example in U.S. Pat. No. 4,636,803 (rectangular block, cylindrical block); U.S. Pat. No. 4,739,339 (cylindrical block); U.S. Pat. No. 5,038,157 (hexagonal bar); U.S. Pat. No. 6,053,608 (tapered lock with a stepped configuration). Further examples of such solid forms are also disclosed in design patents such as U.S. Pat. No. D453,787 issued Feb. 19, 2002. In use, each such block form xe2x80x9cstickxe2x80x9d, xe2x80x9cblockxe2x80x9d, xe2x80x9cbarxe2x80x9d or xe2x80x9cpelletxe2x80x9d is fed into a heated melting device that melts or phase changes the xe2x80x9cstickxe2x80x9d, xe2x80x9cblockxe2x80x9d, xe2x80x9cbarxe2x80x9d or xe2x80x9cpelletxe2x80x9d directly into a print head reservoir for printing as described above.
Conventionally, phase change ink image producing machines or printers, particularly color image producing such machines or printers, are considered to be low throughput, typically producing at a rate of less than 30 prints per minute (PPM). The throughput rate (PPM) of each phase change ink image producing machine or printer employing solid phase change inks in such xe2x80x9cstickxe2x80x9d, xe2x80x9cblockxe2x80x9d, xe2x80x9cbarxe2x80x9d or xe2x80x9cpelletxe2x80x9d forms is directly dependent on how quickly such a xe2x80x9cstickxe2x80x9d, xe2x80x9cblockxe2x80x9d, xe2x80x9cbarxe2x80x9d or xe2x80x9cpelletxe2x80x9d form can be melted down into a liquid. The quality of the images produced depends on such a melting rate, and on the types and functions of other subsystems employed to treat and control the phase change ink as solid and liquid, the imaging member and its surface, the printheads, and the image receiving substrates.
There is therefore a need for a relatively high-speed (greater than xe2x80x9cXXxe2x80x9d PPM) phase change ink image producing machine or printer that is also capable of producing relatively high quality images, particularly color images on plain paper substrates.
In accordance with the present invention, there is provided a pre-melter assembly for containing, conditioning and feeding solid pieces of phase change ink into a melter housing in a phase change ink image producing machine. The pre-melter assembly includes (a) a first portion having a first feeding apparatus and a first container for containing and feeding solid pieces of phase change ink. It also includes a second portion having a second container and a second feeding apparatus for containing and feeding solid pieces of phase change ink to a melter housing. The pre-melter assembly then includes a cooling device mounted in heat exchange relationship with the second feeding apparatus for maintaining a temperature Tw of the solid pieces of phase change ink below a melting point temperature Tm of the solid pieces of phase change ink, thereby preventing premature melting of the solid pieces of phase change ink before the solid pieces reach the melter housing.